Sempron/Athlon64 and AGP - Hardware

This is a discussion on Sempron/Athlon64 and AGP - Hardware ; I am trying to track down a performance issue with my Mythtv install.
Basically, eventhough CPU usage is very low, the video stutters very badly.
The machine that stutters is a Sempron 3000 with an Asus K8V SE mobo
with ...

Sempron/Athlon64 and AGP

I am trying to track down a performance issue with my Mythtv install.

Basically, eventhough CPU usage is very low, the video stutters very badly.

The machine that stutters is a Sempron 3000 with an Asus K8V SE mobo
with an KT800 chipset. I also have a second machine with an Athlon XP
2000+ on a no-name mobo with a Via KT400 chipset that plays video in
Myth just fine.

Both machines have nVidia GPUs with the evil binary drivers, both have
the same kernel (literally, I built my own .deb) and both have scsi drives.

I've been trying to figure out the difference between the two, and I
think I may be on to something; the working machine, which has an Athlon
XP 2000+, does HD just fine with 60% CPU usage. It also uses agpgart...

The non-working machine, the one with the Sempron, locks up when trying
to use agpgart; I have to set option "nvagp" "0" or "1".

On looking at the modules, the working machine loads the agpgart and the
via_agp modules; it has a KT400 chipset.

This option gives you AGP support for the GLX component of X using the
on-CPU northbridge of the AMD Athlon64/Opteron CPUs. You still need an
external AGP bridge like the AMD 8151, VIA K8T400M, SiS755.

So.... First of all, do Semprons have an on-CPU northbridge? Second of
all, should I be loading the via_agp module as well?

Or should I be loading *just* the via_agp?

Or should I slaughter a fatted chicken and lay its entrails on the mobo?
(Personally, I'm about to drive a wooden stake through the d**n thing.)

--Yan

Re: Sempron/Athlon64 and AGP

CptDondo writes:
>The non-working machine loads agpgart and amd64_agp. The kernel docs say:
>
>This option gives you AGP support for the GLX component of X using the
>on-CPU northbridge of the AMD Athlon64/Opteron CPUs. You still need an
>external AGP bridge like the AMD 8151, VIA K8T400M, SiS755.
>
>So.... First of all, do Semprons have an on-CPU northbridge?

All K8s have a northbridge, so your Sempron has one, too.
>Second of
>all, should I be loading the via_agp module as well?

I don't think so (IIRC what the kernel docs say about that). I'm not
using MythTV, but I have the same motherboard and don't have this
module loaded normally. However, I just tried loading it, and it
loaded successfully.

Re: Sempron/Athlon64 and AGP

Anton Ertl wrote:
> CptDondo writes:
>> The non-working machine loads agpgart and amd64_agp. The kernel docs say:
>>
>> This option gives you AGP support for the GLX component of X using the
>> on-CPU northbridge of the AMD Athlon64/Opteron CPUs. You still need an
>> external AGP bridge like the AMD 8151, VIA K8T400M, SiS755.
>>
>> So.... First of all, do Semprons have an on-CPU northbridge?
>
> All K8s have a northbridge, so your Sempron has one, too.
>
>> Second of
>> all, should I be loading the via_agp module as well?
>
> I don't think so (IIRC what the kernel docs say about that). I'm not
> using MythTV, but I have the same motherboard and don't have this
> module loaded normally. However, I just tried loading it, and it
> loaded successfully.
>
> - anton

Does your system load the amd64_agp module?

And, when agpgart loads, what is the size of the agp window? Mine is
stuck at 32MB, no matter what I use in the bios....

I looked through the source code for agpgart, and there doesn't seem to
be an option to set it manually.

Thanks,

--Yan

Re: Sempron/Athlon64 and AGP

CptDondo writes:
>Does your system load the amd64_agp module?

I don't have that module, but I have configured the kernel with

CONFIG_AGP_AMD64=y

So I guess it's as if I had loaded that module.
>And, when agpgart loads, what is the size of the agp window? Mine is
>stuck at 32MB, no matter what I use in the bios....

The kernel says:

agpgart: AGP aperture is 64M @ 0xf8000000
>I looked through the source code for agpgart, and there doesn't seem to
>be an option to set it manually.

Re: Sempron/Athlon64 and AGP

There are a number of things from ... oh, about 2.6.17 or so that work
properly when built as modules, but fail miserably when built directly
in. (CPU frequency scaling and netfilter/iptables support... good
grief.) AGP support for your particular chipset may or may not be one
of those things. If you have the time, you might want to build another
kernel with that set to M and see whether it performs differently.

--
I think it's a beautiful day to go to the zoo and feed the ducks.
To the lions.
--Brian Kantor
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see

Re: Sempron/Athlon64 and AGP

On Mar 6, 3:12 pm, CptDondo wrote:
> I am trying to track down a performance issue with my Mythtv install.
>
> Basically, eventhough CPU usage is very low, the video stutters very badly.
>
> The machine that stutters is a Sempron 3000 with an Asus K8V SE mobo
> with an KT800 chipset. I also have a second machine with an Athlon XP
> 2000+ on a no-name mobo with a Via KT400 chipset that plays video in
> Myth just fine.
>
> Both machines have nVidia GPUs with the evil binary drivers, both have
> the same kernel (literally, I built my own .deb) and both have scsi drives.
>
> I've been trying to figure out the difference between the two, and I
> think I may be on to something; the working machine, which has an Athlon
> XP 2000+, does HD just fine with 60% CPU usage. It also uses agpgart...
>
> The non-working machine, the one with the Sempron, locks up when trying
> to use agpgart; I have to set option "nvagp" "0" or "1".
>
> On looking at the modules, the working machine loads the agpgart and the
> via_agp modules; it has a KT400 chipset.
>
> The non-working machine loads agpgart and amd64_agp. The kernel docs say:
>
> This option gives you AGP support for the GLX component of X using the
> on-CPU northbridge of the AMD Athlon64/Opteron CPUs. You still need an
> external AGP bridge like the AMD 8151, VIA K8T400M, SiS755.
>
> So.... First of all, do Semprons have an on-CPU northbridge? Second of
> all, should I be loading the via_agp module as well?
>
> Or should I be loading *just* the via_agp?
>
> Or should I slaughter a fatted chicken and lay its entrails on the mobo?
> (Personally, I'm about to drive a wooden stake through the d**n thing.)
>
> --Yan

switch xorg.conf to nv driver and see if it helps.

Re: Sempron/Athlon64 and AGP

Dances With Crows writes:
>["Followup-To:" header set to comp.os.linux.hardware.]
>Anton Ertl staggered into the Black Sun and said:
>> CptDondo writes:
>>>Does your system load the amd64_agp module?
>> CONFIG_AGP_AMD64=y
>
>There are a number of things from ... oh, about 2.6.17 or so that work
>properly when built as modules, but fail miserably when built directly
>in. (CPU frequency scaling and netfilter/iptables support... good
>grief.) AGP support for your particular chipset may or may not be one
>of those things.

AGP works fine on my box AFAICT. It's the OP who has a problem (and
modules, but I doubt that's the problem).

Re: Sempron/Athlon64 and AGP

Anton Ertl wrote:
> Dances With Crows writes:
>> ["Followup-To:" header set to comp.os.linux.hardware.]
>> Anton Ertl staggered into the Black Sun and said:
>>> CptDondo writes:
>>>> Does your system load the amd64_agp module?
>>> CONFIG_AGP_AMD64=y
>> There are a number of things from ... oh, about 2.6.17 or so that work
>> properly when built as modules, but fail miserably when built directly
>> in. (CPU frequency scaling and netfilter/iptables support... good
>> grief.) AGP support for your particular chipset may or may not be one
>> of those things.
>
> AGP works fine on my box AFAICT. It's the OP who has a problem (and
> modules, but I doubt that's the problem).

Actually, if it works for you with the AGP stuff built-in but not for
the OP with the AGP stuff as a module, that *could* be the problem. I
use totally different hardware (Intel 7505 chipset) but I know that in
2.6.18 and 2.6.19 the intel_agp support needs to be built-in (*not* as a
module) in order to work on my hardware. When it's built as a module it
never probes to identify the hardware. (The kernels I've tested this on
have been otherwise identical.)

I've tracked my problem to the agp_intel_probe() function not getting
called. It is possible that the corresponding agp_amd64_probe()
function is not getting called either. I'd encourage the OP to build a
new kernel with CONFIG_AGP_AMD64 set to y (not m) and see if that helps.

Until I read this thread, I had been assuming that the bug I found was
specific to Intel hardware, but now you've got me wondering if it
affects other hardware types.